Topcoat/Flowcoat

Applications

Standard Applications

Topcoat resin is designed to be applied in a thin layer to existing fibreglass laminate. Offering abrasion resistance, an aesthetic finish and additional laminate protection standard applications include, but are not limited to:

• Flat roofing: new installations and repairs
• Gutter and gully linings
• Bund wall and base linings
• Storage tank linings & coatings
• Shower and wet room linings

Fibreglass Laminate Ingredients

Topcoat resin first requires a fibreglass laminate surface before application. Fibreglass is created using the following ingredients:

• Polyester Laminating Resin

Polyester laminating resin is designed to be catalysed by MEKP and used in combination with glass fibre chopped strand matting to create fibreglass.

This is unsaturated polyester resin – the term ‘polyester resin’ is used for short. Other terminology may include but is not limited to ‘laminating resin’, ‘grp resin’, ‘fibreglass resin’ and ‘isophthalic resin‘.

• Glass Fibre Reinforcement

Glass fibre CSM is the primary form of fibreglass resin reinforcement. E-glass fibre is industry standard and used across a range of applications. It has excellent wettability and generates a lightweight fibreglass composite when combined with fibreglass resin. It is commonly used for construction, industrial, marine and aerospace work.

Glass fibre is available as 450 gram CSM or 600 gram CSM.

Substrate Application

Topcoat resin application to fibreglass should be performed under carefully controlled conditions. The existing fibreglass surface should be clean, dry and ideally freshly cured. The environment and that for the next 24 – 48 hours should be dry and free from rain. Catalysed resin topcoat should be catalysed with approximately 1 – 4 % MEKP catalyst, which should be carefully mixed. Catalysed resin topcoat should be applied immediately or within a 15-minute window at a target coverage of approximately 0.5 kg per square meter of fibreglass.

Topcoat resin in replacement to fibreglass plus topcoat should be avoided; it is very brittle and lacks the strength of fibreglass.

Ensuring Correct Application

Inexperienced users should follow our guidelines and videos for guidance on laminating.

Resin coating and lining techniques require a degree of skill and understanding in order to create a high-quality finish.

Best results necessitate correct catalyst-resin ratios, prompt application using a paintbrush or polyester roller for larger areas and correct resin coverage per square meter. Work and curing should be performed under clean and dry conditions. Moisture and debris can impact the quality of any cured resin.

More detail can be found below, in the Technical Data Sheet (TDS) or in our instructional guide. Resin Library also supplies step-by-step guides for various polyester resin applications.

Key Processing Information

• Suitability: professional, DIY and hobby usage
  • Odour: Polyester has a strong styrene-based smell
  • Safety Precautions:
    • Wear PPE: gloves, goggles and a mask unless working in a well-ventilated area.
    • Read the MSDS in advance, plan ahead.
    • Consult the MSDS sheet for PPE and safety precautions.
    • Exotherm (Over-Heating)
    • Polyester resin curing is exothermic; it will generate heat as it cures. Work in small, manageable quantities. Mixed resin can overheat and lead to a fire. Do not leave unattended.
  • Users should also be aware of polyester resin hazards. Users should also be aware of how the polyester resin topcoat is controlled under COSHH regulations.
• Recommended working conditions: dry, ambient conditions (15 – 25 ^oC)
• Can be used outside of the aforementioned temperature range but pot-life, cure time and catalyst requirements will be affected.
• Lower operating temperatures are achievable but require modification to catalyst type. Discuss with a Resin Library advisor.
• Resin-Catalyst Mixing Ratio: there are two MEKP catalyst types available for use: a fast-curing for use in temperatures generally below 15 ^oC and slow curing – for use in temperatures above 25 ^oC. Of these, the recommended range is between 1 – 4% MEKP catalyst per unit weight of resin topcoat resin. Concentrations outside of this range will result in a sub-standard laminate.

Quantities

Please note that when dispensing topcoat resin, 1 kg does not equal 1 litre; the density should be accounted for, such that 1 kg of resin would equate to approximately 0.89 litres.

Mixing

• Prepare workable quantities of resin – be aware that excessive amounts of catalysed polyester resin are harder to manage and has a short lifetime: 15 – 30 minutes depending on catalyst amount and resin temperature.
• When adding catalyst, use a dispenser to ensure correct amounts and carefully add to the resin. Mix thoroughly using a clean paddle for 1 – 2 minutes. Take care to avoid introducing air into the mixture.

Application

• Resin should be applied to a cured fibreglass surface at a coverage of approximately 0.5 kg per square meter. This quantity may increase if the surface is non-uniform.
• Apply resin by brush for small or complex areas or a polyester roller for larger areas. Do not use a foam roller as this will dissolve in the resin.
• Allow curing for 12 – 24 hours depending on conditions.

Storage & Pot-Life

• Unopened shelf life of 6 months
• Store at 2 – 20 ^oC in a clean, dark environment.
• Once opened, immediately seal after use. Use within 3 months
• The pot life at 23°C with 1% MEKP Catalyst is 20 minutes. Be sure to use your resin before this time.

Curing Times

• At 15 – 25 °C the resin should take around 10 – 60 minutes to cure depending on the catalyst ratio.
• Full hardness can take 24 hrs.
• Curing can be increased with a higher concentration of catalyst. Do not exceed 4%.

Quality

Manufactured in an ISO9001 compliant environment and used by leading fibreglass roofing brands, Resin Library’s topcoat resin is a high-performance ingredient in many fibreglass applications.

Modifications

Polyester resin is compatible with a variety of ingredients. Flame retardants can be added to obtain B.S. 476 part 6 (fire propagation) and B.S. 476 part 7 (spread of flame). Polyester resin flame retardants are commonly used in combination with polyester-based resin for fibreglass applications.

Research & Development

Much effort has gone into the study of polyester topcoat resins. As a thin, protective barrier designed to protect underlying fibreglass laminate, their applications are broad, centring on the protection of fibreglass roofs and gutters, ponds and water features, bund wall and floor linings, storage tank linings and coatings and other fibreglass composites.

Like standard polyester resin used for laminating, polyester topcoat resin has been the subject of much research and development. Different projects typically necessitate more specific applications and so…

Topcoat resin, referring to the polyester variant applied to fibreglass in this article, can extend to other resin types containing those such as polyurethane and epoxy ingredients.

The compatibility of topcoat resin with water is also a key consideration for water features and pond linings and care should be taken to avoid leaching. More detail on topcoat application has been discussed in regard to paint and surface coatings.

Frequently Asked Questions

Q. What is the difference between topcoat and gelcoat?

A. The topcoat is a finishing paint applied to the external surface of a fibreglass laminate subsequently curing to form a smith, hard surface. Gelcoat is not a finishing paint, rather it is applied to internal moulds and remains mildly sticky/tacky after curing. Polyester resin and glass fibre are generally applied on top of the gelcoat, which eventually cured to form a hard, smooth and glossy finish after release from the mould.

Q. Is a primer needed prior to topcoat application?

A. Topcoat can be applied to fibreglass laminate or onto an existing topcoat surface. In such instances, if there is a of several days or more between the application time and the topcoat application – or if the base surface has been contaminated then some preparation is recommended. This would involve sanding the surface down, removing dust and debris with an acetone wipe and applying a new layer of topcoat as needed.

Q. How do you mix topcoat resin?

A. Topcoat is made from polyester resin. Therefore it requires catalyst (MEKP) to be added in a specific concentration (1 – 4 % v/w) prior to application (concentrations outside of this range will cause inadequate curing). This should be added prior to mixing carefully but thoroughly with a clean mixing instrument. Topcoat should be applied to the intended surface within a 15-minute window to prevent premature curing.

Q. What is the recommended coverage of the resin topcoat?

A. 0.5 kg per square meter is the recommended coverage. A thin, uniform layer should be achieved using a polyester roller. The topcoat should cover all exposed laminate. Glass fibres that are uncoated will pull water into the laminate and cause the fibreglass to fail prematurely.

Q. What happens if too much topcoat is added?

A. If too much topcoat is added, the layer will be prone to cracking, particularly in larger quantities. This will expose the underlying laminate and eventually lead to water ingress and membrane breakdown.

Q. What happens if an insufficient amount of topcoat is added?

A. If too little topcoat is applied, then the fibreglass laminate will be directly exposed to water and external liquids. This could expose any glass fibres to moisture, leading to a breakdown of the laminate. The topcoat is designed to provide an added layer of protection to the laminate and coverage should be thorough.

Q. Is the topcoat safe for ponds?

A. Yes, Resin Library’s topcoat is safe for ponds and other water features. However, once the topcoat has been applied to the fibreglass pond lining, allow it to cure for 24 – 48 hours to allow the styrene content to evaporate. Then rinse down the surface with a hose and allow the water to ‘sit’ for a day or so prior to draining. Repeat this several times before introducing fish.